Internal combustion engines, and more precisely, automotive internal combustion engines, are frequently equipped with one or more camshaft phasers. A purpose of camshaft phasers is to control the timing of a cylinder poppet valve actuating camshafts with respect to the engine's crankshaft. Control of cylinder valve timing, whether applied to intake valves only, or exhaust valves only, or both, is desirable to minimize regulated engine exhaust emissions, while promoting greater fuel efficiency and driveability. Known phasers utilize hydraulic fluid, commonly in the form of engine lubricating oil, to assist in positioning the phaser components relative to one another, while simultaneously positioning the engine's camshaft with respect to the crankshaft.
Those skilled in the art understand that engine lubricating oil may become quite viscous at lower ambient temperatures, particularly when a vehicle is parked with the engine off for periods of time at lower ambient temperatures. Unfortunately, some camshaft phasers exhibit slow response characteristics upon initial startup of a cold engine because oil remaining in the phaser at engine shutdown becomes undesirably viscous.
It would be desirable to provide a system and method for allowing a camshaft phaser's actuating fluid, including, where applicable, engine lubricating oil, to circulate through a phaser prior to activation of the phaser during an engine operating event, so as to allow to the phaser, and more importantly, the oil in the phaser, to be warm and hence, properly responsive to the commands of the engine controller.